Thermosetting coating composition useful as chip resistant primer II

ABSTRACT

Novel epoxy-polyester graft copolymer and novel, solvent-based thermosetting coating composition comprising said copolymer and blocked polyisocyanate crosslinking agent. Coating composition may be formulated as hot sprayable, high solids coating composition suitable for use as chip resistant automotive vehicle primer adapted for use on body panel areas subject to chipping by stones, gravel and other road debris. Alternatively, composition may be formulated as a high solids composition sprayable with conventional spraying equipment. Epoxy-polyester graft copolymer is prepared by polymerization of lactone monomers in presence of hydroxy functional epoxy resin precursor. Precursor resin is formed by reaction of diepoxide, previously chain extended with diphenol, with hydroxy functional secondary amine in chain terminating reaction.

TECHNICAL FIELD

This invention relates to a novel epoxy-polyester graft copolymer and toa novel, solvent-based, thermosetting coating composition comprisingsame. It relates also to such coating composition formulated, forexample, as a hot sprayable, high solids coating composition suitablefor use as a chip resistant automotive vehicle primer adapted for use onbody panel areas subject to chipping by stones, gravel and other roaddebris.

BACKGROUND

Automobile manufacturers, in their efforts to extend the expected lifeof automobile sheet metal and the like, have directed considerableattention to various processes and compositions designed to result innot only improved corrosion resistance but also improved chip resistanceproperties. In particular, research and development efforts haverecently been directed to obtaining primer compositions which areflexible and chip resistant and which give corrosion protection whileexhibiting good humidity and solvent resistance, as well as goodintercoat adhesion. New automobile designs and concern about chipping inareas exposed to stones, gravel and other road debris, e.g. rockerpanels, have demanded such chip resistant primers which can be appliedin reasonable thicknesses by techniques which do not require extensiveand expensive processing modifications during painting operations. Todata available primers, whether high or low solids, have not provensuitable.

In order to overcome the aforementioned chipping problem it has beencommon to apply relatively thick chip resistant coatings in body panelregions, which are inclined to chip, prior to application of stillanother primer composition. One such chip resistant sealer materialwhich has been employed is a solvent based polyvinyl chloride plastisolsealer which has been applied with airless spraygun equipment inthicknesses of about 20 mils in regions subject to high levels ofchipping. Problems attendant with such thick coatings are readilyapparent. Because of the thickness in the region to which it is applied,these materials present an appearance problem often resulting inwaviness and roughness in the final coating on the sheet metal. Oftentimes surface imperfections also result from the fact that a primer isapplied over the top of this sealer, with the primer and sealer beingcured together. As a result some solvent and plasticizer tend to bedriven out of the polyvinyl chloride plastisol and result in a wavy andrough surface. Still further problems associated with the use of suchpolyvinyl chloride plastisol sealers and the like involve applicationtechnique. Since the polyvinyl chloride plastisol sealers and the likemust be applied in thicknesses of 20 mils or greater in order to obtaingood adhesion, they cannot be feathered down to blend in with otherregions of the sheet metal which do not require the additional chipprotection. Thus, the materials must be applied using a maskingtechnique whereby those regions which are not to be coated with thesealer material are masked in a separate operation prior to applicationof sealer. This masking is then removed after the sealer is applied. Itwould obviously be desirable to eliminate these additional steps in theapplication of the chip resistant sealer material.

Accordingly, it is a preferred object of this invention to provide anovel solvent based, thermosetting coating composition adapted for useas a chip resistant primer, which primer may be applied in thicknessesof less than 20 mils and which may be feathered in such a manner as toblend with paint in other areas of the substrate to be painted which donot require chip resistant coating.

It is a further object of the present invention to provide novel resinssuitable for use in solvent-based thermosetting coating compositions. Inthis regard, it is a particular object of the invention to providenovel, epoxy-polyester graft copolymer resins which are crosslinkableduring cure, on the surface of a substrate.

It is another object of the invention to provide novel coatingcompositions which comprise crosslinkable epoxy-polyester graftcopolymers and blocked polyisocyanate crosslinking agent and whichprovide high crosslinking efficiency and hard, well cured films atminimum bake temperatures such as applied to automotive primers. In thisregard, it is a particular object of the invention to provide a novelepoxy-polyester/blocked polyisocyanate thermosetting coating compositionof sufficiently low Volatile Organic Content (VOC) to meet governmentalguidelines and yet which can be applied to a substrate by spraying orother known method.

It is still another object of the invention to provide a compositionwhich will form a coating on a substrate, which coating has advantageousphysical properties including, for example, humidity and solventresistance, flexibility and corrosion protection for the underlyingsubstrate.

Additional aspects and advantages of the invention will be apparent fromthe following description thereof.

DISCLOSURE OF THE INVENTION

According to the present invention, novel crosslinkable epoxy-polyestergraft copolymer resins are provided which are adapted for use inthermosetting coating compositions, and which are especiallyadvantageous for use in high solids and chip resistant, organic solventbased thermosetting coating compositions. The epoxy-polyester graftcopolymer resins of the invention preferably have a number averagemolecular weight (Mn) of about 2,000 to about 20,000 and are prepared bypolymerization of lactone monomers in the presence of hydroxy functionalepoxy resin precursor preferably having a number average molecularweight (Mn) of between about 1,000 and about 4,000 and itself beingformed by reaction of diepoxide, which has been chain extended withdiphenol, with hydroxy functional secondary amine in chain terminatingreaction.

Also according to the present invention, a novel, organic solvent based,thermosetting resin/crosslinking agent composition, in addition tosolvent and any pigments and additives such as, for example, catalyst,flow control agents and the like, comprises the epoxy-polyester graftcopolymer resin of the invention and blocked polyisocyanate crosslinkingagent including, but not limited to, blocked trifunctional isocyanuratering containing polyisocyanates and oligoester modified blockedisocyanates.

Particularly preferred compositions of the invention are thoseformulated as high solids coating compositions having solids levels inthe range of 65-80% solids and which are applied as chip resistantprimers in those areas of automotive panels, such as rocker panels,which are exposed to high levels of chipping. Such compositions may beapplied in thicknesses ranging from 1 to 25 mils wet to obtain finalcoatings in the range of 1 to 12 mils dry, and may be feathered down toblend in with paint applied to regions outside that requiring additionalchip resistance protection. Generally, the compositions of this solidslevel may be applied using hot spray equipment at temperatures in therange of 140°-160° F.

Other preferred compositions of the invention are those formulated ashigh solids coating compositions adapted to be applied by conventionalspraying onto a substrate. These high solids coating compositions mayhave a solids level in the range of 50-60% and are especially useful asa primer coating on the bare, unpolished metal surface of an automotivevehicle. As used herein, a high solids coating composition is one havinga volatile organic content of about 479 g/l (4.0 lb./gal.) or less.

Other features and advantages of this invention will become moreapparent from the following, detailed description thereof including thepreferred embodiments and best mode of carrying out this invention.

DETAILED DESCRIPTION OF THE INVENTION

More specifically, the invention relates to a novel epoxy-polyestergraft copolymer adapted for use in a thermosetting composition and to athermosetting composition comprising that graft copolymer and a blockedpolyisocyanate crosslinking agent.

The novel, epoxy-polyester graft copolymer preferably has a numberaverage molecular weight (Mn) of between about 2,000 and about 20,000and is formed by polymerization of lactone monomers in the presence ofhydroxy functional epoxy resin precursor preferably having a numberaverage molecular weight (Mn) of between about 1,000 and about 4,000.The hydroxy functional epoxy resin precursor is formed by reactingdiepoxide, which has been chain extended with diphenol, with hydroxyfunctional secondary amine in chain terminating reaction inapproximately 1 to 1 equivalent ratio. The polymerization of lactonemonomers with the precursors is generally carried out at a temperaturebetween about 130° C. and about 200° C. and the polymerization reactionmixture preferably comprises between about 10 and about 80 weightpercent said hydroxy functional epoxy ester resin precursor and betweenabout 20 and about 90 weight percent said lactone monomers.

Thermosetting compositions of the invention comprise the above graftcopolymer and blocked polyisocyanate crosslinking agent comprising atleast one isocyanate group which has been blocked by reaction with anactive hydrogen bearing blocking agent. The blocked polyisocyanatecrosslinking agent is included in the composition in an amount such thatupon deblocking of the blocked isocyanate groups thereof at the curetemperature of the composition, the crosslinking agent provides betweenabout 0.5 and about 1.6 reactive isocyanate groups per reactive group onthe epoxy-polyester graft copolymer.

Each of the above major components of the compositions as well as othercomponents and other aspects of the invention are described hereinafterin greater detail.

A. EPOXY POLYESTER GRAFT COPOLYMER

As described above this copolymer is prepared by polymerizing lactonemonomer in the presence of an hydroxy functional epoxy resin precursorformed by reacting diepoxide, which has been chain extended withdiphenol, with hydroxy functional secondary amine in chain terminatingreaction.

It is believed to be a significant characterizing aspect of theepoxy-polyester graft copolymer of the invention that the polymerizedlactone portion of the epoxy-polyester graft copolymer gives the polymerflexibility as well as toughness, two key properties when choosing aprimer for use in areas susceptible to chipping. It is a furthercharacterizing aspect of the copolymer that it includes epoxy resinportions, i.e. hydroxyl terminated epoxy resin precursor is used as aninitiator to form the graft copolymer, which give the copolymerexcellent corrosion resistance properties. Still further, because thegraft copolymers of the invention are branched they require a minimumamount of crosslinking in order to obtain a suitable network for goodcoating integrity. Since crosslink bonds, e.g. isocyanate bonds as usedin compositions of the invention, tend to be somewhat brittle, it isdesirable to keep the number of such bonds to a minimum. Even stillfurther it is a characterizing aspect of the invention that the graftcopolymer contains tertiary amine groups (i.e., since hydroxy functionalsecondary amines are used to form the hydroxy functional epoxy resinprecursor, tertiary amine groups are present in the final copolymer).Tertiary amine groups are excellent catalysts for the isocyanatecrosslinking reaction used to cure compositions of this invention.

Preferred epoxy-polyester graft copolymers of the invention includesignificant aromatic content which is believed to enhance corrosionresistance properties. Even though aromatics tend to increase thebrittleness of polymers and compositions including such polymers, it ispossible to include them since, as mentioned above, the polymerizedlactone portion of the epoxy-polyester graft copolymer gives the polymerincreased flexibility which more than compensates for any suchbrittleness. A particular preferred embodiment of the epoxy-polyestergraft copolymer resin of the invention is prepared from aromaticcontaining diepoxide which is extended with diphenol. In addition, it ispresently understood that the phenolic oxygens introduced into theepoxy-polyester graft copolymer resin by the chain extension reaction ofepoxy with phenol advantageously provide excellent adhesion to metalsubstrates, for example steel.

Each of the reactants employed in the preparation of the epoxy-polyestergraft copolymer is described in greater detail below.

(i) Chain Extended Diepoxide Reactant

The chain extended diepoxide reactant suitable for preparing the epoxyresin precursor used in preparation of the epoxy-polyester graftcopolymer can be any of numerous chain extended diepoxides includingmany which are commercially available and which will be apparent to theskilled of the art in view of the present disclosure. While, ultimately,the choice of diphenol chain extended epoxy reactant for preparing theepoxy precursor resin will depend to an extent upon the particularapplication intended for the coating composition, terminal diepoxides,that is chain extended diepoxides bearing two terminal epoxide groups,are generally most preferred. These are generally more reactive andtherefore require reaction conditions under which undesirable sidereactions, for example, epoxy-epoxy reactions and gelation, can be moreeasily avoided.

Preferably, the chain extended diepoxide has a number average molecularweight (Mn) between about 1,200 and about 3,500, and more preferablybetween about 1,600 and about 2,400. Numerous diepoxides extended withdiphenol are commercially available. These include certain of the wellknown bisphenol-A epichlorohydrin epoxy resins of the Epon (trademark)series, Shell Chemical Company, Houston, Tex., (e.g. Epon 1001 and Epon1004) and the DER (trademark) series, Dow Chemical Company, Midland,Mich. These diglycidyl ether bisphenol-A resins or higher molecularweight analogs thereof, are preferred in view of their cost andcommercial availability.

Any of the commercially available diphenol extended epoxies such asthose discussed above may be further extended, if desired, by diphenolin order to give higher molecular weight materials having desirableproperties.

Still further, other diepoxy resins, not previously extended withdiphenol may be extended with diphenol and used in the preparation ofthe epoxy resin precursor. Preferred diepoxy resins of this type includeEpon 828 (trademark) and Epon 829 (trademark) which are nonextendeddiepoxides of the aforementioned Epon Series, as well as cycloaliphaticdiepoxy resins such as: the Eponex (trademark) series, Shell ChemicalCompany, Houston, Tex.; hydantoin epoxy resins such as, for example,Resin XB2793 (trademark), Ciba-Geigy Corporation, Ardsley, N.Y.; and anyof a wide variety of acyclic or cyclic aliphatic diepoxides such as, forexample, 1,4-butanediol diglycidyl ether and 4-vinylcyclohexene dioxideand the like. Other suitable diepoxides, either previously extended withdiphenol or not so extended, are available and will be apparent to theskilled of the art in view of the present disclosure. Also, it will beunderstood from the foregoing that any mixture of compatible extendeddiepoxides may be used.

The diphenol reactants suitable for reaction with a diepoxide reactantin chain extension reaction, in those instances where initial or furtherextension with diphenol are required, include numerous commerciallyavailable materials, many of which will be readily apparent to theskilled of the art in view of the present disclosure. Preferreddiphenols have the general formula (I): ##STR1## wherein R is a divalentlinking moiety substantially unreactive with the diepoxide resin.Preferably R is a divalent organic linking moiety, for example (CH₂)_(n)where n is preferably from about 1 to about 8, C═O, and the like,although inorganic moieties, for example sulfonyl and the like, are alsosuitable. Diphenols of this character have been found to provide goodreactivity with diepoxides described above and to provide, ultimately,cured coatings of the invention having excellent physical properties,most notably excellent corrosion protection. It will be apparent to theskilled of the art in view of the present disclosure that R should besubstantially unreacted with the hydroxy functional secondary amineemployed in preparation of the epoxy ester resin precursor. Particularlypreferred diphenols include those according to formula (I) above,wherein R is selected from the group comprising a straight or branchedalkylene or alkylidene moiety of one to about 10 carbons, preferablyhaving three to four carbons and most preferably having the generalformula ##STR2## wherein R' and R" are the same or different and each isa monovalent organic moiety preferrably selected from the groupcomprising hydrogen and lower alkyl, of about one to four carbons, mostpreferably one or two carbons, and the like or a mixture of any of them.Preferably the diphenol has a number average molecular weight (Mn)between about 180 and about 500, more preferably between about 180 andabout 250. Such diphenols include, for example biphenol-A, which is mostpreferred, bisphenol-B and the like and a compatible mixture of any ofthem. As used herein the term diphenol may include, for example,compounds comprising a single dihydroxy substituted phenyl ring such asbenzenediol. More preferred, however, are those diphenols providing twoterminal, mono-hydroxy substituted phenyl rings such as in formula (I),above. Other examples of diphenols are bis-(4-hydroxy-tertbutylphenyl)-2,2-propane, bis-(2-hydroxy-naphthyl)-methane and1,5-dihydroxynaphthalene. Other suitable diphenols for the epoxy resinprecursor of the present invention will be apparent to the skilled ofthe art in view of the present disclosure.

(ii) Hydroxy Functional Secondary Amine Reactant

The hydroxy functional secondary amine which is reacted in chainterminating reaction with the reaction product of the above detaileddiepoxide and diphenol may be selected from a broad class of aliphatic,cycloaliphatic and aromatic hydroxy functional amines.

Numerous such amines, which may bear mono- or dihydroxy functionalitywill be apparent to those skilled in the art. Exemplary of such aminesare those having the formula ##STR3## wherein R and R' are selected fromthe group consisting of aliphatic, cycloaliphatic and aromatic radicalswhich will not interfere with either the chain termination reactionbetween the chain extended diepoxide and the hydroxy functionalsecondary amine or the polymerization of lactone monomers in thepresence of the hydroxy functional epoxy resin precursor.

R and R' in the above formula may be the same or different, butpreferably should be of the same nature. X may be selected from hydrogenand hydroxyl radical.

While the hydroxyl group on R and/or R' may be other than primary,primary hydroxyls are preferred since such primary hydroxyl groupsprovide preferred reaction sites for polymerization of lactone monomers.If secondary hydroxyl group bearing amines are employed, for example,polymerization of lactone at the ends of the precursor would notnecessarily be predominant as preferred since there will be secondaryhydroxyls present on the extended diepoxide which will compete with theterminal hydroxyls to initiate lactone polymerization. Even in thosecases where primary hydroxyl is present on the amine, lactone monomerswill polymerize at hydroxyl sites other than those at the ends of theamine terminated precursor. Up to 20% or more would not be unexpected.

Examples of preferred radicals R and R' for the hydroxy functional amineof the above formula are:

    --CH.sub.2 --.sub.n

where n=1-5;

    --CH.sub.2 CH.sub.2 O--.sub.n CH.sub.2 CH.sub.2 --

where n=1-12; ##STR4## where n=1-12; and ##STR5## where n=1-12Preferably R and R' are methylene, ethylene, or lower alkylene groupsbut they may be any other noninterfering radical including those, forexample, such as benzyl, oxyalkylene, etc.

Particularly preferred primary hydroxyl bearing amines for use inpreparing the hydroxy functional epoxy precursor are diethanol amine,methylethanol amine, dipropanol amine, and methylpropanol amine.

The hydroxy functional epoxy resin precursor used to initiate lactonepolymerization in the preparation of the epoxy-polyester graft copolymerof the invention can be made according to techniques well known to theskilled of the art. The chain extension, where necessary, and chaintermination reactions occur sequentially, with the chain extension ofthe diepoxide being carried out first. Diepoxide and diphenol arecharged into a suitable reactor and heated. It should be recognized thatto assure rapid and/or more conplete reaction of the diepoxide with thephenol functionality, it is usually preferred to have a catalystpresent. The use of catalyst, however, has been found to provideadvantageous epoxy resin precursor of the invention and is preferred.Epon 829 (trademark), mentioned above, as sold, provides a proprietarycatalyst. Epon 828 (trademark), is substantially the same but does notprovide such catalyst. Suitable catalysts are commercially available andinclude, any of the well known catalysts for epoxy-phenol reactions.

After completion of the above chain extension reaction that hydroxyfunctional secondary amine reacted is charged into the reaction vessel.This reaction is exothermic and drives itself to completion.

As noted above, the chain extended reaction product is reacted withhydroxy functional secondary amine in chain terminating reaction inapproximately 1 to 1 equivalent ratio. This ratio is desirable sinceexcess epoxy could result in gelation of the reaction mixture, whileexcess amine remaining in the reaction mixture could compete with epoxyresin precursor for lactone monomers during formation of theepoxy-polyester graft copolymer. For this reason, if excess amine isused during formation of the precursor; it should preferably be removedprior to reaction of the precursor with lactone monomers.

(iii) Lactone Monomers

The lactone reactant may be any lactone, or combination of lactones,having at least six carbon atoms, for example, from six to eight carbonatoms, in the ring and at least one hydrogen substituent on the carbonatom which is attached to the oxy group in said ring. In one aspect, thelactone used as a reactant can be represented by the general formula:##STR6## in which n is at least four, for example, from four to six, atleast n+2R's are hydrogen, and the remaining R's are substituentsselected from the group consisting of hydrogen, alkyl, cycloalkyl,alkoxy and single ring aromatic hydrocarbon radicals. Lactones havinggreater numbers of substituents other than hydrogen on the ring, andlactones having five or less carbon atoms in the ring, are consideredunsuitable for the purposes of the invention because of the tendencythat polymers thereof have to revert to the monomer, particularly atelevated temperature.

The lactones preferred in this invention are the epsilon-caprolactoneshaving the general formula: ##STR7## wherein at least six of the R's arehydrogen and the remainder are hydrogen, alkyl, cycloalkyl, alkoxy orsingle ring aromatic hydrocarbon radicals, none of the substituentscontain more than about twelve carbon atoms, and the total number ofcarbon atoms in the substituents on a lactone ring does not exceed abouttwelve. Unsubstituted epsilon-caprolactone, in which all the R's arehydrogen, is derived from 6-hydroxyhexanoic acid and is most preferred.Substituted epsilon-caprolactones, and mixtures thereof, are availableby reacting a corresponding substituted cyclohexanone with an oxidizingagent such as peracetic acid.

Among the substituted epsilon-caprolactones considered most suitable forthe purposes of the invention are the various monoalkylepsilon-caprolactones such as the monomethyl-, monoethyl-, monopropyl-,monoisopropyl-, etc. to monododecyl epsilon-caprolactones; dialkylepsilon-caprolactones in which the two alkyl groups are substituted onthe same or different carbon atoms, but not both on the epsilon carbonatom; trialkyl epsilon-caprolactones in which two or three carbon atomsin the lactone ring are substituted, so long as the epsilon carbon atomis not distributed; alkoxy epsilon-caprolactones such as methoxy andethoxy epsilon-caprolactones; and cycloalkyl, aryl, and aralkylepsilon-caprolactones such as cyclohexyl, phenyl and benzylepsilon-caprolactones.

Lactones having more than six carbon atoms in the ring, e.g.,zeta-enatholactone and eta-caprylolactone may also be polymerized inaccordance with the method of the invention.

Polymerization of the lactones in accordance with this invention iscarried out in conventional manner in that the polymerization isinitiated by reaction with a compound having at least one reactivehydrogen capable, with or without the aid of a catalyst, by opening thelactone ring and adding it as an open chain without forming water ofcondensation--in this case the initiator compound being the hydroxyfunctional epoxy precursor described above.

To initiate and continue the polymerization of the lactone, the lactoneand the initiator (i.e., the precursor) are preferably heated to atemperature between about 130° and 200° C. in order to achieve apractical and desirable rate of reaction with a minimum ofdecomposition. The temperature may be considerably lower however, i.e.,as low as about 50° C. at the sacrifice of speed of reaction. It mayalso be considerably higher, i.e., up to about 300° C., although caremust be taken at such higher temperatures because of the more likelylosses, at temperatures above 250° C., due to decomposition ofundesirable side reactions. Generally, therefore, a temperature range of50° to 300° C. is considered operable and a more limited range betweenabout 130° and 200° C. is considered preferable.

The polymerization may be, and preferably is, carried out with the useof a catalyst, such as a basic or neutral ester interchange catalyst, toaccelerate the reaction. Among catalysts suitable for this purpose aresuch metals as lithium, sodium, potassium, rubidium, caseium, magnesium,calcium, barium, strontium, zinc, aluminum, titanium, cobalt, germanium,tin, lead, antimony, arsenic and cerium, as well as the alkoxidesthereof. Additional suitable catalysts are, by way of example, thecarbonates of alkali- and alkaline earth metals, zinc borate, leadborate, zinc oxide, lead silicate, lead arsenate, litharge, leadcarbonate, antimony trioxide, germanium dioxide, cerium trioxide,cobaltous acetate and aluminum isopropoxide. Catalyst concentrationsbetween about 0.001 and 0.5%, based on the weight of the startinglactones, are suitable. The preferred range is from 0.01 to 0.2%.

The epoxy polyester graft polymerization products obtained in accordancewith the invention have molecular weights generally upwards of about2,000 and preferably within the range of about 4,000 to about 20,000,although molecular weights below and substantially above this range areobtainable if desired. They also have reactive terminal hydroxyl orcarboxyl groups, the number of reactive terminal groups depending uponthe functionality of the initiator. They are characterized by thepresence of series of interconnected, substantially linear units orgroups composed of carbon, hydrogen and oxygen. The interconnected unitsare opened lactone residues each having a terminal oxy group at one end,a carbonyl group at the other end, an intermediate chain of at leastfive carbon atoms and at least one hydrogen substituent on the carbonatom in the intermediate chain that is attached to the terminal oxygroup. The oxy group of one lactone residue is connected to the carbonylgroup of an adjacent lactone residue in the series and the oxy group ofthe last lactone residue in a series is connected to a hydrogen to forma terminal hydroxyl group at one end of the series.

B. CROSSLINKING AGENT

The crosslinking agent employed in the novel solvent based coatingcomposition of the invention comprises blocked polyisocyanate. The novelsolvent based coating compositions of the invention, as a result ofemploying blocked polyisocyanate crosslinking agents, exhibitexceptional shelf stability even when corrosion inhibiting pigments suchas zinc chromate are used in high concentrations.

As used herein "blocked polyisocyanate" means an isocyanate compoundcontaining two or more isocyanato groups, all of which have been reactedwith a material which will prevent reaction of the isocyanate group atroom temperature with compounds that conventionally react with suchgroups, and at least some of which will permit that reaction to occur athigher (cure) temperatures. In general the blocked polyisocyanate may beprepared by reacting a sufficient quantity of an active hydrogencontaining blocking agent with the polyisocyanate to insure that no freeisocyanato groups are present. The blocking agent may be represented bythe formula BH and may be selected from numerous materials, hereinafterdiscussed, which bear an active hydrogen.

The blocked polyisocyanate crosslinking agent is included incompositions of the invention in amounts such that upon deblocking ofthe blocked isocyanato groups at the cure temperature of thecomposition, the crosslinking agent will provide between about 0.5 andabout 1.6, preferably between about 0.8 and about 1.3, reactiveisocyanato groups per reactive group on the film forming resin of thecoating composition as described above. Blocked polyisocyanates ofnumerous types may be employed in the compositions of the invention.Particularly suitable blocked polyisocyanates, which will be discussedfurther hereinafter, include blocked polymethylene polyphenolisocyanates, isocyanurate ring containing blocked polyisocyanates andcertain oligoester modified blocked polyisocyanates.

In the preparation of the blocked polyisocyanate crosslinking agent, anysuitable organic polyisocyanate may be used. Representative examples arethe aliphatic compounds such as trimethylene, tetramethylene,pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene,2,3-butylene, 1,3-butylene, ethylidine and butylidene diisocyanates; thecycloalkylene compounds such as 1,3-cyclopentane, 1,4-cyclohexane, and1,2-cyclohexane diisocyanates; the aromatic compounds such asm-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene, and1,4-naphthalene diisocyanates, the aliphatic-aromatic compounds such as4,4'-diphenylene methane, 2,4- or 2,6-tolylene, or mixtures thereof,4,4'-toluidine, and 1,4-xylylene diisocyanates; substituted aromaticcompounds such as dianisidine diisocyanate, 4,4'-diphenyletherdiisocyanate and chlorodiphenylene diisocyanate; the triisocyanates suchas triphenyl methane-4,4'4"-triisocyanate, 1,3,5-triisocyanate benzeneand 2,4,6-triisocyanate toluene; the tetraisocyanates such as4,4'-diphenyl-dimethyl methane-2,2',5,5'-tetraisocyanate; and thepolymerized polyisocyanates such as tolylene diisocyanate dimers andtrimers, and the like.

In addition, the organic polyisocyanate may be a prepolymer derived froma polyol including polyether polyol or polyester polyol, includingpolyethers which are reacted with excess polyisocyanates to formisocyanate-terminated prepolymers. The polyols may be simple polyolssuch as glycols, e.g., ethylene glycol and propylene glycol, as well asother polyols such as glycerol; trimethylolpropane, pentaerythritol, andthe like, as well as mono-ethers such as diethylene glycol, tripropyleneglycol and the like and polyethers, i.e., alkylene oxide condensates ofthe above. Among the alkylene oxides that may be condensed with thesepolyols to form polyethers are ethylene oxide, propylene oxide, butyleneoxide, styrene oxide and the like. These are generally calledhydroxyl-terminated polyethers and can be linear or branched. Examplesof polyethers include polyoxyethylene glycol, polyoxypropylene glycol,polyoxytetramethylene glycol, polyoxyhexamethylene glycol,polyoxynonamethylene glycol, polyoxydecamethylene glycol,polyoxydodecamethylene glycol and mixtures thereof. Other types ofpolyoxyalkylene glycol ethers can be used. Especially useful polyetherpolyols are those derived from reacting polyols such as ethylene glycol,diethylene glycol, triethylene glycol, 1,4-butylene glycol, 1,3-butyleneglycol, 1,6-hexanediol, and their mixtures; glycerol, trimethylolethane,trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol,dipentaerythritol, tripentaerythritol, polypentaerythritol, sorbitol,methyl glucosides, sucrose and the like with alkylene oxides such asethylene oxide, propylene oxide, their mixtures, and the like.

A particular class of aromatic polyisocyanates which may be employed inthe novel solvent based coating compositions of the invention arepolymethylene polyphenol isocyanates having the formula: ##STR8##wherein n equals 1 to 3. The compounds, sold under the tradename "PAPI"by the Upjohn Chemical Company of Kalamazoo, Mich., have proven to beparticularly useful in compositions of the invention, resulting incompositions exhibiting desirable toughness in the final cured coating.

The active hydrogen containing blocking agents which are reacted withthe above described organic diisocyanates may be selected from numerousblocking agents which will be apparent to those skilled in this art.Representative of the blocking agents which are preferred are thoseselected from the group consisting of (i) aliphatic, cycloaliphatic andaromatic alkyl monoalcohols; (ii) hydroxyl amines; (iii) oximes; (iv)lactams; and (v) triazoles. Any suitable aliphatic, cycloaliphatic oraromatic alkyl monoalcohol may be used as a blocking agent in accordancewith the present invention. For example, aliphatic alcohols, such asmethyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl,nonyl, 3,3,5-trimethylhexyl, decyl, and lauryl alcohols, and the likemay be employed. Suitable cycloaliphatic alcohols include, for example,cyclopentanol, cyclohexanol and the like, while aromatic-alkyl alcoholsinclude phenylcarbinol, methylphenylcarbinol, and the like. Minoramounts of even higher molecular weight relatively non-volatilemonoalcohols may be used, if desired, to serve as plasticizers in thecoatings provided by the invention. Examples of hydroxyl amines whichmay be employed as blocking agents include ethanol amine and propanolamine. Suitable oxime blocking agents include, for example,methylethylketone oxime, acetone oxime and cyclohexanone oxime. Examplesof lactams which may be used as blocking agents are -caprolactam,-butyrolactam and pyrrolidone, while suitable triazoles includecompounds such as 1,2,4 triazole, 1,2,3 benzotriazole, 1,2,3 tolyltriazole and 4,5 diphenyl-1,2,3 triazole. Particularly preferred activehydrogen containing blocking agents are methylethyl ketoxime and2-ethylhexanol.

(i) Isocyanurate Ring Containing Blocked Isocyanate Compounds

Within the scope of the above general class of blocked polyisocyanatecrosslinking agents, a particular class type of blocked polyisocyanatecrosslinking agent which may be employed in the novel solvent basedcoating compositions of the invention comprises isocyanurate ringcontaining blocked isocyanate compounds. In general, these blockedpolyisocyanates may be formed by blocking with the aforementionedblocking agent isocyanurate ring containing polyisocyanates. Thesecompounds may be formed by cyclotrimerization of difunctionalisocyanates. Usually, the reaction does not stop in this stage andcontinues through the formation of polyfunctional oligomers or a mixtureof such oligomers with a portion of the pure trifunctionalpolyisocyanate. Mixtures of trifunctional product and variouspolyfunctional oligomers are commercially available.

A particularly desirable blocked polyisocyanate crosslinking agent isthe blocked form of the pure trifunctional isocyanurate represented bythe following formula: ##STR9## wherein R is selected from the groupconsisting of aliphatic, cycloaliphatic and aromatic groups andcombinations thereof and B is the residue of an active hydrogencontaining blocking agent. More specifically, this compound is disclosedin copending application Ser. No. 368,178 filed Apr. 14, 1982, thedisclosure of which is hereby incorporated by reference.

(ii) Oligoester Modified Blocked Polyisocyanates

Still further particular blocked polyisocyanates useful as crosslinkingagents in the novel solvent based coating compositions of this inventionare oligoester modified blocked polyisocyanates prepared from aparticular class of oligoester diols and triols. A first type of sucholigoester modified blocked polyisocyanates is prepared from organicdiisocyanates bearing one isocyanato group more reactive than the other,with the more reactive isocyanato first being blocked with a blockingagent and the remaining isocyanato group then being reacted withhydroxyl functionality of an oligoester diol or triol as referred toabove. The second type of oligoester modified blocked polyisocyanate maybe prepared by reacting oligoester diols from the aforementioned classof oligoesters with an excess of organic diisocyanate so as to form anisocyanato terminated prepolymer followed by blocking of the terminalisocyanato groups of the prepolymer with an active hydrogen containingblocking agent. Each of these materials is particularly useful in thecompositions of the invention and produces final cured coatingcompositions exhibiting outstanding flexibility.

Oligoesters of the type employed in the preparation of thesecrosslinking agents are described in U.S. Pat. No. 4,322,508 issued Mar.30, 1982, the disclosure of which is hereby incorporated by reference.The hydroxy functional oligoesters within the useful class of materials(i) have a number average molecular weight (Mn) of between about 150 andabout 3000, preferably between about 230 and about 1000, (ii) bear 2 or3 hydroxyl groups per molecule, and (iii) are formed by anesterification reaction between a carboxylic acid and an epoxide. Theesterification reaction products are selected from the group consistingof:

(a) the esterification reaction product of polycarboxylic acid, i.e.,carboxylic acid bearing 2 or more carboxyl groups, and monoepoxide;

(b) the esterification reaction product of polyepoxide, i.e., a compoundhaving 2 or more epoxide groups, and monocarboxylic acid, preferablycontaining no ethylenic unsaturation, and bearing no hydroxyfunctionality;

(c) the esterification reaction product of hydroxy functional carboxylicacid and mono- or polyepoxide, preferably monoepoxide;

(d) the esterification reaction product of monocarboxylic acid andhydroxyl functional mono- or polyepoxide, preferably monoepoxide; and

(e) mixtures of (a)-(d).

As noted above, the first type of oligoester modified blockedpolyisocyanate crosslinking agent is prepared by (i) reacting organicdiisocyanate bearing one isocyanato group which is more reactive thanthe other with a sufficient amount of an active hydrogen containingblocking agent to react substantially with all of the more reactiveisocyanate groups, thus providing a half-blocked diisocyanate and (ii)reacting this half-blocked intermediate with the above discussedoligoester. The organic diisocyanates employed in this synthesis, aswell as the active hydrogen containing blocking agents, are discussedabove in connection with the preparation of the isocyanurate ringcontaining blocked isocyanate crosslinking agents useful in compositionsof the invention. The organic polyisocyanate-blocking agent adductintermediate is formed by reacting a sufficient quantity of the blockingagent with the organic diisocyanate to insure that one of the two --NCOgroups on the diisocyanate is reacted. The reaction between the organicdiisocyanate and the blocking agent is exothermic; therefore, thediisocyanate and the blocking agent are preferably admixed attemperatures no higher than about 80° C., preferably below about 50° C.,to minimize the exothermic effect.

This intermediate is next reacted with the oligoester diol or trioldescribed above so as to react substantially all free or unblockedisocyanato groups of the diisocyanate/blocking agent intermediate withhydroxyl groups of the oligoester. This reaction is carried outdesirably at a temperature of about 80°-120° C.

As also discussed above, the second type of oligoester modified blockedpolyisocyanate crosslinking agent useful in the novel solvent basedcoating compositions of the invention is prepared by reacting an excessof organic diisocyanate withh an oligoester diol from the abovedescribed class of oligoesters followed by reaction of the terminalisocyanato groups formed on the resultant prepolymer with an activehydrogen containing blocking agent as described above so as to reactwith substantially all the isocyanato groups. The diisocyanate startingmaterial is used in excess in amounts sufficient to insure that theintermediate is isocyanate terminated. Therefore, it is preferable thatthe organic diisocyanates and the dihydroxy functional oligoester bereacted in a molar ratio of from greater than 1:1 up to 2:1. Numerousdiisocyanates of the type described hereinbefore may be employed in thepreparation of this intermediate. While it is not necessary that oneisocyanato group be more reactive than the other, the preparation ofthis type of crosslinking agent does not preclude the use of suchmaterial.

C. GENERAL DISCUSSION--OTHER ASPECTS OF INVENTION AND OTHER COMPONENTS

The coating compositions of the invention have been found to provide acured coating having the advantageous physical properties describedabove, over a wide range of cure temperatures and a wide range of solidslevels. More specifically, the coating compositions according topreferred embodiments of the invention have been found to cure attemperatures from as low as about 120° C. or less within about 15minutes or less, and yet to cure and suffer no significant loss ofadvantageous physical properties at temperatures as high as about 200°C. or more for periods up to about 60 minutes or more. Consideredtogether with the storage stability of the coating composition, it canbe readily recognized that the present invention provides a highlysignificant advance in the coating composition art.

It will be within the skill of the art to determine the proper volatileorganic content for a given coating composition of the invention and fora given application. Preferred solvents have relatively low volatilityat temperatures appreciably below their boiling points such that solventevaporation is low during storage and/or application of the coatingcomposition to the substrate. A suitable solvent system may include, forexample, toluene, methyl ethyl ketone, isobutyl acetate, xylene,cellosolve acetate, acetone and a mixture of any of them. Other solventswhich may be employed include terpenes, aliphatic and aromatic naphthas,and the like. Additional suitable solvents are commercially availableand will be apparent to the skilled of the art in view of the presentdisclosure.

Any solvent allowed to remain in the cured coating should be inert so asto avoid adverse effect upon the cured coating or upon another coatinglayer used in conjunction with it during the curing process orthereafter. Preferrably, the cured coating is substantially free ofsolvent.

Sufficient solvent is used to reduce the viscosity of the coatingcomposition to a level suitable for application to the substrate in thedesired manner.

Obviously, in those cases where the composition is to be applied as achip resistant primer the amount of solvent will be reduced so as togive a solids level of about 65-80%. Such higher solids materials aregenerally applied using hot spray equipment.

Flow control agent(s), for example, polybutyl acrylate; wettingagent(s), for example, silicone; pigments; pigment dispersants;corrosion inhibitors, for example, chromate pigments, numerous of all ofwhich are known to the skilled of the art, may be employed in thecoating compositions of the invention. In addition, suitable reactiveadditives can be used, including, for example, low molecular weight diolflow control agents and reactive diluents.

Compositions of the invention, and in particular the chip resistantprimers of the invention, may also include anti-settling or anti-saggingagents to control the thixotropic properties of the composition.Exemplary of available materials suitable for this purpose are Dislon(trademark) 6900-20X manufactured by Kusumoto Chemicals, Ltd., Tokyo,Japan and sold by King Industries, Norwalk, CT 06852; Bentone(trademark) 38, N.L. Industries, Highstown, N.J. 08520; and Cab-O-Sil(trademark) M-5, Cabot Corporation.

Curing the coating composition requires baking for sufficient time atsufficiently elevated temperature to react the crosslinking agent withthe hydroxyl functionality of the epoxy polyester graft copolymer. Thetime and temperature required to cure the coating are interrelated anddepend upon the particular epoxy polyester resin, crosslinking agent,solvent and other materials, if any, and the amount of each comprisingthe coating composition. The coating compositions according to preferredembodiments of the invention, as described above, have been found toprovide the best coating results when cured at temperature at about 150°C. (300° F.) for 20 minutes. It is a highly significant advantage of theinvention, however, that these same coating compositions can withstand,for example, temperature as high as about 200° C., (390° F.) for periodsof time as long as about 60 minutes. Accordingly, great flexibility isprovided in both designing and implementing a curing schedule for partscoated with the coating compositions of the invention. Thus, in theassembly of automotive vehicles, for example, vehicles unavoidably heldin a curing oven for long periods of time during unplanned assembly lineshut-downs are recovered with cured and unharmed coatings.

High solids coating compositions according to the present invention,comprising the novel crosslinkable epoxy polyester graft copolymer ofthe invention, especially the preferred resins described above andblocked polyisocyanate crosslinking agent, especially the preferredmaterials described above have been found to afford cured coatings withimproved corrosion resistance and chip resistance, thus representing ahighly advantageous advance in the art.

A most preferred use of the coating composition of the invention is as ahigh solids hot sprayable chip resistant primer for use on a bare metalsubstrate such as an automotive vehicle body which is subject tochipping. Primer compositions typically are pigmented and any pigmentscommonly included in primer compositions for metal substrates andacrylic dispersion topcoats such as, for example, carbon block, ironoxide, lithopone, magnesium, silicate, silica, barium sulfate, TiO₂,chrome yellow, calcium chromate, strontium chromate, zinc potassiumchromate any the like may be used. The primer can be pigmented accordingto known methods including, for example, by grinding pigments in aportion of the curable resin and adding to the primer composition.

The pigment-to-binder ratio of the chip resistant primer may be as muchas 0.5/1 to 2/1 by weight, respectively; it is preferred, however, touse a primer having a pigment-to-binder ratio of about 1:1-1.5:1 byweight, respectively.

In preferred embodiments of this invention pigments and thixotropicagents desirably are dispersed with epoxy ester resins which do not havean elastomeric component as does the epoxy-polyester graft copolymeremployed as the primary film forming resin of the compositions of thisinvention. It has been found that, in addition to being very effectivedispersing agents for the preparation of pigment millbases andthioxtropic dispersions, non-elastomeric epoxies give the compositionstoughness. One type of epoxy useful for this purpose comprises thereaction product of diepoxide, dimer acid and a mixture of soya fattyacid and propionic acid (See Example 6). Other epoxy ester resins usefulfor this purpose are those disclosed in copending application Ser. Nos.448,886 filed June 14, 1982, 431,465 filed Sept. 30, 1982 and 430,182filed Sept. 30, 1982, all assigned to the assignee of this application.These resins comprise the simultaneous reaction product of diepoxidewith (i) diphenol, dicarboxylic acid or a mixture of them in chainextension reaction and (ii) fatty acid in chain terminatingesterification reaction. Still other suitable epoxy resins useful fordispersing pigment and thixotropic agents will be apparent to theskilled of the art.

No special expedients are necessary in formulating the primercompositions of this invention. For example, they may be prepared byincorporating the resinous components in a suitable solvent system.Thus, for example, by suitable mixing or agitation, each resinouscomponent may be dissolved in a solvent and the resulting solutioncombined to form finished primer compositions.

The solvent system may be any suitable combination of organic solventsas described above. For a high solids, hot sprayable, automotive vehiclechip resistant primer, the solvent will comprise preferably about 20 toabout 40 percent by weight of the total coating composition, although ofcourse, larger or smaller amounts may be utilized depending upon thesolids content desired.

The primer is generally maintained at about 65 to about 80 percentsolids content for hot spraying purposes with conventional thinners suchas aromatic hydrocarbons, commercial petroleum cuts which areessentially aromatic, and the like, and sprayed on to the metal base andcured. The primer is applied in greater thickness of 1 to 25 mils wet,preferably 10 to 25 mils wet, in order to obtain final coatings in thedesired range of 5-11 mils dry in regions highly susceptible to chippingand is then feathered down in thickness to the thickness of paints inareas not receiving a chip resistant primer. The primer is cured atelevated temperatures by any convenient means such as baking ovens orbanks of infra-red heat lamps. Curing temperatures are preferably fromabout 135° C. to about 165° C., although curing temperatures from about100° C. to about 230° C. may be employed, if desired.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that the specific examplesare presented by way of illustration and not by way of limitation.Unless otherwise specified, all references to "parts" are intended tomean parts by weight.

EXAMPLE 1 Preparation of Epoxy-Polyester Graft Copolymer

Into a suitable reactor were charged 519 parts Epon 829 and 204 partsbisphenol A. The temperature of the mixture was brought up to about 180°C., at which point an exothermic reaction took place that raised thetemperature to about 200° C. After one hour, the WPE was 1150. Themixture was cooled to 150° C., 92 parts diethanolamine and 700 partsM-pyrol were added to the mixture at which point a mild exothermicreaction took place that raised the temperature to about 150° C. Afterone hour, 1513 parts epsilon-caprolactone and 10 parts dibutyltin oxidewere added to the mixture. A second mild exothermic reaction occurredthat raised the temperature to about 150° C. The progress of thereaction was followed by viscosity measurement; the reaction was stoppedat J-L viscosity (25 parts mixture and 21 parts M-pyrol producing a50.0% solids solution). At that point, 554 parts M-pyrol were added andthe mixture was cooled.

EXAMPLE 2 Preparation of Epoxy-Polyester Graft Copolymer

Into a suitable reactor were charged 519 parts Epon 829 and 204 partsbisphenol A. The temperature of the mixture was brought up to about 180°C. at which point an exothermic reaction took place that raised thetemperature to about 200° C. After one hour, the WPE was 750. Themixture was cooled to 150° C.; 66 parts M-methylethanolamine and 197parts M-pyrol were added to the mixture at which point a mild exothermicreaction occurred and the temperature rose to about 150° C. After onehour, 1475 parts epsilon-caprolactone and 10 parts dibutyltin oxide wereadded to the mixture. A second mild exotherm took place that raised thetemperature to 120° C. The progress of the reaction was followed byviscosity measurement; the reaction was stopped at J-L viscosity (25parts mixture and 21 parts M-pyrol producing a 50.0% solids solution).At that point, 554 parts M-pyrol were added and the mixture was cooled.

EXAMPLE 3 Preparation of Epoxy-Polyester Graft Copolymer

Into a suitable reactor were charged 562 parts Epon 829 and 188 partsbisphenol A. The temperature of this mixture was raised to about 170°C., at which point an exothermic reaction took place that raised thetemperature to about 190° C. After one hour, the WPE was 560-640. Themixture was cooled to 150° C., 130 parts diethanolamine and 220 partsM-pyrol were added to the mixture at which point a mild exothermicreaction took place that raised the temperature to about 150° C. Afterone hour, 1634 parts epsilon-caprolactone and 2 parts dibutyltin oxidewere added to the mixture. A second mild exothermic reaction occurredthat raised the temperature to about 160° C. The reaction was held twohours at 160° C. at which point its progress was checked by bothviscosity measurement and % NV determination. It was stopped at Sviscosity (25 parts mixture and 38 parts M-pyrol producing a 60.0%solids solution). At that point, 410 parts M-pyrol were added and themixture was cooled. The resulting resin had a Z₄ -Z₅ viscosity at 80.0%solids.

EXAMPLE 4 Preparation of Epoxy-Polyester Graft Copolymer

Into a suitable reactor were charged 552 parts Epon 829 and 248 partsbisphenol A. The temperature was raised to about 135° C. and allowed toexotherm slowly to 180° C. After one hour the WPE was 1100-1250. Themixture was cooled to 150° C., 71 parts diethanolamine and 217 partsM-pyrol were added to the mixture at which point a mild exothermicreaction took place that raised the temperature to about 150° C. Afterone hour, 1486 parts epsilon-caprolactone and 2 parts dibutyltin oxidewere added to the mixture. A second mild exothermic reaction occurredthat raised the temperature to about 160° C. The reaction was maintainedat 170° C. for two hours at which point its progress was checked by bothviscosity measurement and % solids determination. It was stopped at Vviscosity (25 parts mixture and 38 parts M-pyrol producing 60.0% solidssolution). At that point, 355 parts M-pyrol were added and the mixturewas cooled. The resin had a Z₆ -Z₇ viscosity at 80.0% solids.

EXAMPLE 5 Preparation of Epoxy-Polyester Graft Copolymer

Into a suitable reactor were charged 813 parts Epon 829 and 358 partsbisphenol A. The temperature of the mixture was brought up to about 180°C., at which point an exothermic reaction took place that raised thetemperature to about 230° C. After one hour, the WPE was 1200-1400. Themixture was cooled to 150° C., 106 parts diethanolamine and 230 partsSolvesso 100 were added to the mixture at which point a mild exothermicreaction took place that raised the temperature to about 150° C. Afterone hour, 1916 parts epsilon-caprolactone and 8 parts dibutyltin dioxidewere added to the mixture. A second mild exothermic reaction occurredthat raised the temperature to about 160° C. The progress of thereaction was followed by viscosity measurement; the reaction was stoppedat G viscosity (25 parts mixture and 47 parts Xylene producing a 50.0%solids solution). At that point, 347 parts Solvesso 100 were added andthe mixture was cooled. The resulting resin had a Z₇ viscosity at 85.0%N.V.

EXAMPLE 6 Preparation of Epoxy-Ester Dispersing Resin

Into a suitable reactor were charged 1380 parts Epon 829, 954 partsEmpol 1016, 364 parts soya fatty acid, 268 parts 2,2bis(hydroxymethyl)propionic acid, and 13 parts lithium neodecanoate. Thetemperature of the mixture was brought up to about 180° C., at whichpoint an exothermic reaction took place that raised the temperature toabout 200° C. After one hour, the acid number was found to be less than2. 940 parts Solvesso 100 and 305 parts Solvesso 150 were added, and themixture was cooled. The resin had a viscosity of Z₇ at 70.0% N.V.

EXAMPLE 7 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor were charged 780 parts methylethyl ketoxime and180 parts Solvesso 100. 1330 parts of PAPI 27 was added dropwise to themixture over two hours; the reaction temperature rose from roomtemperature to 80°-95° C. 39 parts 2-ethylhexanol was added to themixture and the temperature of the mixture was maintained at 85°-95° C.for one hour. At that point, 816 parts of M-pyrol was added and themixture was cooled. The resulting resin was dark brown and had aviscosity of 6000 cps at 75.0% solids.

EXAMPLE 8 Preparation of Blocked Polyisocyanate Crosslinking Agents

Into a suitable reactor were charged 537 parts methylethyl ketoxime. 784parts PAPI 94 was added dropwise over two hours; the reactiontemperature rose from room temperature to 85°-95° C. After 30 minutes,the mixture was checked to insure complete reaction of the isocyanate byinfrared. If residual isocyanate was detected, additional methylethylketoxime could be added to mixture. At that point, 300 parts methylamylketone and 150 parts M-pyrol were added and the mixture was cooled.

EXAMPLES 9-12 Preparation of Blocked Polyisocyanate Crosslinking Agent

Blocked isocyanate crosslinkers according to the invention were preparedin the manner of Example 8. The components employed are shown in thetable below.

    ______________________________________                                                      Example                                                         Composition     9      10       11   12                                       ______________________________________                                        L-2291 A*       360    360      360                                           Desmodur IL*                         525                                      methyl amyl ketoxime                                                                          174                   87                                      benzotriazole          238                                                    epsilon-caprolactam             227                                           N--methyl pyrolidone                                                                          133    150      195  461                                      % NV             80    80.1     75.1  57                                      Viscosity       Z.sub.1                                                                              Z.sub.6  Z.sub.2                                                                            Z                                        ______________________________________                                         *Trademarks of Mobay Chemical Co.; L2291 A is a biurette of hexamethylene     diisocyanate; Desmodur IL is a polyisocyanurate of tolylene diisocyanate.

EXAMPLE 13 Millbase Preparation

In a one gallon can or ballmill were charged the following materials andone quart of diagonal shot. The mixture was placed on a roller mill for16-24 hours to reach a 7+ hegman dispersion. At that point, the letdownwas added, and the mixture was run an additional hour on the rollermill.

    ______________________________________                                        Hi-Sol #3*           585                                                      2-Ethyl Hexanol      95                                                       Polyethylene Wax     70                                                       Anti-Terra-U**       40                                                       Resin of Example 6   103                                                      Barytes              2259                                                     TiO.sub.2            429                                                      Carbon Black         29                                                       Strontium Chromate   143                                                      Letdown: Resin of Example 6                                                                        247                                                      ______________________________________                                         *Trademark of Ashland Chemical Co., Columbus, Ohio; HiSol #3 is an            aromatic solvent.                                                             **Trademark of Byk Mallinckrodt, Wallingford, CT 06492; AntiTerra-U is an     antisettling and wetting agent.                                          

EXAMPLE 14 Bentone Gel Preparation:

To a clean Ball Mill, charge the following:

    ______________________________________                                                               Parts                                                  ______________________________________                                        Solvesso 150             513                                                  Propylene Carbonate      13                                                   Bentone 38               30                                                   Grind 30 minutes, then add:                                                   Resin of Example 6       384                                                  Grind approximately 2 Hrs. to 8 Hegman                                        Letdown with:                                                                 Hi-Sol #3                60                                                                            1000                                                 ______________________________________                                    

    ______________________________________                                        Coating Compositions                                                                       Example                                                          Composition    15     16     17   18   19   20                                ______________________________________                                        Resin of Example 1                                                                           2635                                                           Resin of Example 2    2284   2284                                             Resin of Example 3                2241                                        Resin of Example 4                     2141                                   Resin of Example 5                          2015                              Millbase of Example 13                                                                       5788   5788   5788 5788 5788 5788                              Bentone Gel of Example                                                                       2315   2315   2315 2315 2315 2315                              14                                                                            Crosslinker of Example 7                                                                      984    984         984  984  984                              Crosslinker of Example 8     1050                                             Dislon (trademark)                                                                            114    114    120  120 --    120                              Cab-O-Sil (trademark)                                                                         142    142                                                    ______________________________________                                    

The coating compositions were prepared by sequential mixing in a 5gallon working capacity EMCO Proto-Lab SW Mill (trademark), Epworth Mfg.Co., South Haven, Mich., set at 900 rpm. Resin and Dislon were firstmixed for approximately 10 minutes and then millbase, Bentone gel andcrosslinker were added sequentially while mixing. Finally Cab-O-Sil wasadded and the composition mixed until a grind of 6+ on the Hegman scalewas obtained.

The above compositions were sprayed at 140°-160° C. using hot-sprayequipment commercially available from Nordson Corp. UnpolishedBronderite steel panels were sprayed and baked at 135° C. for 20minutes. The thickness of the coating tested varied from 5 mils to 12mils. The panels were top-coated with white enamel and tested for chipresistance using 10 pts. of gravel in the gravelometer test. All theabove compositions exhibited excellent chip resistance. In addition,panels were tested for corrosion resistance (500 hrs. salt spray test,scribed panels) and humidity resistance with excellent results.

Additional coating compositions according to the invention are shownbelow.

    ______________________________________                                                    Example                                                           Composition   21     22         23   24                                       ______________________________________                                        Resin-Ex. 4   2141   2141       2141 2141                                     Millbase-Ex. 13                                                                             5788   5788       5788 5788                                     Gel-Ex. 14    2315   2315       2315 2315                                     X-linker-Ex. 9                                                                               922                                                            X-linker-Ex. 10       922                                                     X-linker-Ex. 11                  984                                          X-linker Ex. 12                      1294                                     Dislon         100    100        100  100                                     ______________________________________                                    

In view of this disclosure, many modifications of this invention will beapparent to those skilled in the art. It is intended that all suchapparent modifications fall within the true scope of this invention andbe included within the terms of the appended claims.

INDUSTRIAL APPLICABILITY

It will be apparent from the foregoing that this invention hasindustrial applicability as a coating composition, especially as a hotsprayable, high solids coating composition suitable for use as a chipresistant automotive vehicle primer adapted for use on body panel areassubject to chipping by stones, gravel and other road debris.

What is claimed is:
 1. A novel, epoxy-polyester graft copolymer adaptedfor use in a thermosetting composition, which copolymer has a numberaverage molecular weight (Mn) of between about 2,000 and about 20,000,said copolymer being prepared by polymerization of lactone monomers inthe presence of hydroxy functional spray resin precursor having a numberaverage molecular weight (Mn) of between about 1,000 and about 4,000 andbeing formed by reacting diepoxide, which has been chain extended withdiphenol, with hydroxy functional secondary amine in chain terminatingreaction in approximately 1 to 1 equivalent ratio, wherein saidpolymerization of said lactone monomers is carried out at a temperaturebetween about 130° C. and about 200° C. and the polymerization reactionmixture comprises between about 10 and about 80 weight percent saidhydroxy functional epoxy resin precursor and between about 20 and about90 weight percent said lactone monomers.
 2. The epoxy-polyester graftcopolymer of claim 1 wherein said lactone monomers polymerized to formsaid graft copolymer are selected from those represented by the generalformula: ##STR10## in which n is at least 4, at least n+2 R's arehydrogen, and the remaining R's are substituents selected from the groupconsisting of alkyl, cycloalkyl, alkoxy and single ring aromatichydrocarbon radicals.
 3. An epoxy-polyester graft copolymer inaccordance with claim 2 wherein said lactone monomers areepsilon-caprolactone monomers having the general formula: ##STR11##wherein at least 6 of the R's are hydrogen and the remainder areselected from the group consisting of alkyl, cycloalkyl, alkoxy andsingle ring aromatic hydrocarbon radicals, wherein none of thesubstituents contain more than about 12 carbon atoms, and the totalnumber of carbon atoms in the substituents on a lactone ring does notexceed about
 12. 4. An epoxy-polyester graft copolymer in accordancewith claim 3 wherein said epsilon-caprolactone monomers compriseunsubstituted epsilon-caprolactone.
 5. An epoxy-polyester graftcopolymer in accordance with claim 2 wherein said polymerization of saidlactone monomers is carried out in the presence of catalyst.
 6. Anepoxy-polyester graft copolymer in accordance with claim 1 wherein saidhydroxy functional secondary amine employed in the preparation of saidhydroxy functional epoxy resin precursor has the formula: ##STR12##wherein, R and R' are selected from the group consisting of aliphatic,cycloaliphatic and aromatic radicals which will not interfere witheither the chain termination reaction between said chain extendeddiepoxide and said hydroxy functional secondary amine or saidpolymerization of said lactone monomers, and X is selected from thegroup consisting of hydrogen and hydroxyl radical.
 7. An epoxy-polyestergraft copolymer in accordance with claim 6 wherein said hydroxyfunctional secondary amines employed in the preparation of said hydroxyfunctional epoxy resin precursor bear primary hydroxyl functionality. 8.An epoxy-polyester graft copolymer in accordance with claim 7 whereinsaid hydroxy functional secondary amines employed in the preparation ofsaid hydroxy functional epoxy resin precursor are selected from thegroup consisting of diethanol amine, methylethanol amine, dipropanolamine and methylpropanol amine.
 9. An epoxy-polyester graft copolymer inaccordance with claim 1 wherein said chain extended diepoxide employedin the preparation of said hydroxy functional epoxy resin precursor isformed by chain extending with diphenol, diepoxide selected from thegroup consisting of bisphenol-A epichlorhydrin epoxy resin, hydantoinepoxy resin, cyclic and acyclic aliphatic diepoxides, and a mixture ofany of them.
 10. An epoxy-polyester graft copolymer in accordance withclaim 1 wherein said diphenols used to chain extend said diepoxide havethe general formula: ##STR13## wherein R is a divalent, organic, linkingmoiety substantially unreactive with the epoxy functionality of saiddiepoxide.
 11. An epoxy-polyester graft copolymer in accordance withclaim 10 wherein said diphenols are selected from the group consistingof bisphenol-A, bisphenol-B and a compatible mixture of any of them. 12.An epoxy-polyester graft copolymer in accordance with claim 1 wherein(a)said lactone monomers which are polymerized are epsilon-caprolactonemonomers selected from the group consisting of those having the formula##STR14## wherein at least6 of the R's are hydrogen and the remainderare selected from the group consisting of alkyl, cycloalkyl, alkoxy andsingle ring aromatic carbon radicals, wherein none of the substituentscontain more than about 12 carbon atoms and wherein the total number ofcarbon atoms in the substituents on the lactone ring does not exceedabout 12; (b) said epsilon-caprolactone monomers are reacted in thepresence of a catalyst; (c) said hydroxy functional secondary amineemployed in preparation of said hydroxy functional epoxy resinprecursors have the general formula: ##STR15## wherein R and R' areselected from the group consisting of aliphatic, cycloaliphatic andaromatic radicals which will not interfere with either the chaintermination reaction of said diepoxide and said hydroxy functionalsecondary amine or said polymerization of said lactone monomers, X isselected from the group consisting of hydrogen and hydroxyl radicals,and at least a portion of the hydroxyl groups on said hydroxy functionalsecondary amine are primary; and (d) said chain extended diepoxide isformed by chain extending diepoxide selected from the group consistingof bisphenol-A epichlorohydrin epoxy resin, hydantoin epoxy resin,cyclic and acyclic aliphatic diepoxide, and a mixture of any of themwith diphenols selected from the group consisting of those having thegeneral formula: ##STR16## wherein R is a divalent, organic, linkingmoiety substantially, unreacted with the epoxy functionality of saiddiepoxide.